Read the shipment record: The gym says it never received your cancellation
Locate the exact cancellation method in the agreement and the proof showing when and where you sent the request.
Open the right case: The gym says it never received your cancellation
Resend through the documented channel if necessary and ask the gym to acknowledge the effective cancellation date in writing. Keep delivery, email, portal or in-person receipt evidence.
Confirm the case is closed: The gym says it never received your cancellation
You have a written acknowledgement or account state showing the membership is cancelled and the last authorised billing date.
Escalate with shipment evidence: The gym says it never received your cancellation
If the gym keeps charging despite a valid documented cancellation, complain to the provider in writing and use the consumer-protection or payment-dispute route appropriate to your country and payment method.